Iron carbonyl-cyclopentadiene complexes



IRON CARBONYL-CYCLOPENTADIENE COMPLEXES Claims priority, application Great Britain January 9-, 1953 7 Claims. (Cl. 260-439) This invention relates to organic derivatives of iron, and to a process for the production of complexes of iron carbonyls with cyclopentadienes or substituted cyclopentadienes.

The trend in the design of modern high-speed internal combustion engines is toward ever higher compression ratios. It has been found that with every rise in compression ratio, there must be a corresponding increase in the octane number and anti-knock characteristics of the fuel employed. Ordinary gasolines obtained from the refining of crude oils do not possess the necessary characteristics, hence it has become common practice to employ various additives to the fuels available to increase their octane number and anti-knock characteristics to an acceptable level.

In the past, numerous organo-metal compounds have been suggested as fuel additives for improving the antiknock characteristics of the fuel. For many years, the more or less standard additive has been tetraethyl lead. However, this compound as a fuel additive has certain serious drawbacks: it is expensive to produce, is rather toxic to humans, and its efiiciency as an anti-knock agent is substantially reduced by the presence of sulfur-containing compounds in the fuel employed. As a substitute for tetraethyl lead, it has been proposed to use certain metal carbonyls, particularly the carbonyls of iron, cobalt and nickel. These compounds, however, have been found to be particularly unsatisfactory as fuel additives, for they are very unstable in the presence of light and oxygen, and they are quite volatile at usual engine operating temperatures. Such compounds are difiicult to handle, lose their efficiency as anti-knock agents rapidly and present a serious explosion hazard.

Recently, it has been proposed to employ another class of organo-metal compounds as anti-knock additives and :to employ these additives in a different manner. It has Ibeen found that various cyclopentadienylderivatives of certain metals impart desirable anti-knock properties to lubricants to which they are added. In particular, it has been found that ferrocenes (dicyclopentadienyl iron and its substitution products), when added to motor lubricants in small amounts, significantly lower the apparent octane number of the fuel required by the motor in order that its design output can be achieved. These compounds and their utility have been disclosed in copending application Serial No. 307,010, and therein the benefits to be derived from their use as anti-knock additives are clearly demonstrated.

It has now been discovered that complexes of iron carbonyls with cyclopentadiene or substituted cyclopentadienes possess highly desirable properties as anti-knock agents when added to either the fuel or the lubricant used by the engine, and form a new class of organo-metallic compounds suitable for that purpose. The precise structure of these complexes has not been determined, but it is believed that they are coordination complexes of the general formula Fe(CO) (R) where R is a cyclopentadienyl or substituted cyclopentadienyl.radical.

2 These complexes may be prepared by stirring and heating together in an autoclave a mixture of an iron carbonyl with cyclopentadieneor a substituted cyclopenta diene until reaction ceases. It is preferred that the iron carbonyl employed be iron pentacarbonyl (Fe(CO) The temperature throughout this process must be carefully controlled to prevent decomposition of the complex and to reduce undesirable side reactions.

The symbol R in the above formula represents the cyclopentadienyl or a substituted cyclopentadienyl radical. In these latter radicals the substituent may be any essentially hydrocarbon group. By the term essentially hydrocarbon group is meant an unsubstituted hydrocarbon group or a substituted hydrocarbon group in which the substituent does not significantly alter the basically hydrocarbon characteristics of the group. Examples of the hydrocarbon substituent include alkyl groups such as methyl, ethyl, propyl, normaland secondary-butyl, pentyl and hexyl groups, their homologs, analogs and isomers; substituted alkyl groups such as halogenated alkyl groups, oxygen-containing alkyl groups such as hydroxy-substituted alkyl groups, carbalkoxy groups, keto groups, alkyl carboxylic acid and ester groups and the like; substituted and unsubstituted aryl, alkaryl and aralkyl groups including phenyl, benzyl and tolyl groups, and the corresponding substituted derivatives.

Examples of the compounds which may be reacted with iron carbonyl to form the desired complexes are: cyclopentadiene, S-ethyl-1,3-cyclopentadiene, S-isopropyl cyclopentadiene, S-n-butyl cyclopentadiene 5-(sec-butyl)cyclopentadiene, n-hexyl cyclopentadieneg, S-(beta-chloropropionyl)-1,3 -cyclopentadiene; 4,5 -diethyl-l ,3 -cyclopentadiene; S-phenyl-l,3-cyclopentadiene; 5-benzyl1,3-cyclopentadiene; 4,5-dichloro-1,3-cyclopentadiene; S-ethoxy- 1,3 -cyclopentadiene; 2-methyl-4-ethyl-1,3 -cyclopentadiene; 1,2,3,4 tetraphenyl-1,3 cyclopentadiene; 1,4 dirnethyl- 2,3,5-triphenyl-1,3-cyclopentadiene, and the like. 7

The complexes are prepared by introducing iron carbonyl and the cyclopentadienyl reactant into an autoclave and stirring the mixture thoroughly until the reaction ceases, meanwhile maintaining the mixture at a temperature of from about C. to about 200 C. It is preferred that the reaction mixture temperature be carefully maintained in the range of from about C. to about 180 C.

Although the presence of oxygen in the reactor atmosphere does not inhibit the formation of the complexes, the desired reaction goes forward most efficiently if the atmosphere in which it is conducted contains no oxygen. Thus, in the preferred practice of the invention substantially all of the oxygen is purged from the reactor before the reaction is started. It is preferred that nitrogen constitute the inert atmosphere and it is still more preferable that the cyclopentadienyl reactant, if it be gaseous at the temperature and pressure at which reaction is carried out, constitute all or at least a major portion of the atmosphere in which the reaction is conducted. The reaction may also be effected in a liquid-full reactor, there being substantially no atmosphere of any kind. v The reaction may be carried out at the vapor pressur the desired complex varies with the particular reactants.

used, the pressure employed and the reaction mixture temperature. Ingeneral, it has been found that the desired degree of reaction occurs within about 4-7 hours, al-

though n semec s s, a t astwo hours has has.

Patented Aug, .4, 9.

quired and in other cases the reaction time has been as much as 16 hours.

The amount of the cyclopentadienyl reactant present in the. reaction theatre should be at least that amount stoichiometrically equal tothe' amount of iron carbonyl present. It is preferred that the cyclopentadienyl reactant be present in excess of the theoretical amount," the amount of excess preferably lyingwithin the range of from about 0.1 mole to about 4 moles, and still more preferably in the range of from about 0.5 mole to about 2.0 moles per mole of iron carbonyl charged into the reactor. It is desirable that the cyclopentadienyl reactant be present in such excess that its vapors constitute at least a major part of the atmosphere within which the reaction is carried out. If necessary, additional amounts of this reactant may be added to the reaction theatre from time to time during the course of the reaction.

The crude product may be separated from the reaction mixture by extraction of that mixture with a suitable solvent, such as petroleum spirits, cold ether, or the like. The purified complex may then be obtained from the crude product by recrystallization from cold ether or by sublimation in a vacuum.

These complexes themselves have been found to possess highly desirable properties as anti-knock agents when added to either the fuel or. the lubricant used by the engine, and form a new class of organo-metallic compounds suitable for that purpose.

It has further been discovered that ferrocenes may be prepared by the thermal decomposition of these complexes. This decomposition is efiected easily and smoothly to give excellent yields of the desired product by heating the corresponding complex in an autoclave in an inert atmosphere at a temperature somewhat in excess of that required for the formation of the complex.

The following conditions are to be met in conducting the decomposition:

a. The atmosphere in the autoclave preferably does not contain any oxygen and the atmosphere in the reactor must be inert with respect to the reactants and the reaction products. While nitrogen is suitable as the atmosphere, it is preferred that all or at least a major portion of the atmosphere in which the reaction is conducted consist of the gaseous cyclopentadiene or substituted cyclopentadiene from which the particular complex employed was derived.

b. The temperature at which the decomposition is effected must be above the decomposition temperature of the particular complex employed, but must be below the decomposition temperature of the corresponding ferrocene compound. The temperature is further dependent upon the pressure maintained upon the reaction system and the composition of the atmosphere in which the reaction is conducted. In general, the decomposition is most efliciently conducted at a temperature within the range of from about 150 C. to about 400 C., and it is preferred that the reaction mixture temperature be maintained within the range of from about 180 C. to about 250 C.

c. The decomposition may be effected under pressure, it may be conducted at the vapor pressure of the reactants, or it may be accomplished under reduced pressure. In the preferred practice of the invention, the decomposition is conducted at the vapor pressure of the reactants, the atmosphere consisting predominantly of the particular cyclopentadienyl compound from which the complex was derived. The decomposition may be carried out in a liquidfull reactor, there being substantially no atmosphere pres-' ent.

d. The reaction time is dependent upon the particular reactants involved, the pressure applied to the reaction system, the temperature of the reaction mixture andthe nature of the atmosphere in which the reaction is conducted. In general, the decomposition is generally sub stantially complete in from about 3 hours to about 15 hours. It is preferred that the reaction mixture be heated for at least 5 hours, and in general it is undesirablethat the heating continue for more than 10 hours.

If found desirable, the decomposition may be conducted in the presence of a liquid diluent which is a solvent for the reactants and reaction products. The solvent must be inert with respect to both the reactants and the reaction products. It is preferred that the solvent be one whose vapor pressure at the temperature and pressure employed is very small compared to the total pressure of the reaction system. An example of a suitable solvent is mineral white oil. The concentration of the reactants in the solvent-reaction medium mixture is not a critical factor, and may be varied Within relatively wide limits. The practical limits of the concentration of the reactants in the solvent are determined by the relative solubility of the initial reactants and the reaction products in the particular solvent employed.

The following examples are presented for the purpose of illustrating the invention. It is to be-understood that the invention is not intended to be restricted to the specific illustrative examples below and that other specific modifications are included in the invention. The parts referred to are parts by weight, unless otherwise stated, the

relation to parts by weight to parts by volume being that of the kilogram to the litre.

Example I allowing to cool, the volatile reaction products were Vented and the crude reaction mixture was obtained as a crystalline sol-id contaminated with a small amount of dark colored viscous liquid. This reaction mixture was filtered and washed repeatedly with cold ether and finally I recrystallized from petroleum ether. The pure complex compound was obtained in the form of violet crystals, melting point l93-l94 C., in a yield of 81% by weight based on the iron pentacarbonyl employed. Its analysis agreed with the empirical formula Fe C H O Example 11 205.5 parts of iron pentacarbonyl and parts of cyclopentadiene were mixed in an autoclave and the air was displaced from the vessel by nitrogen. The autoclave was closed and heated at 160 C. for 6 hours. After allowing to cool, the volatile reaction products were vented and the crude reaction products were filtered. 13.6 parts of iron carbonyl were recovered from the fil trate. The residue was washed with petroleum spirit and dried in a vacuum. The yield of the crude complex compound was 98% by weight based on the iron carbonyl actually consumed in the reaction.

The crude complex compound was purified by sublimation in a vacuum to yield the pure product having a melting point of 193194 C. and an analysis corresponding with the empirical formula Fe C H O Example III 21.7- parts of the iron carbonyl-cyclopentadiene complex prepared in Example I were placed in an autoclave, which was evacuated to 0.1 mm. mercury pressure and then sealed. The autoclave was heated to 220 C. for 9 hours and then allowed to cool slowly. The reaction products were extracted with acetone, the extract evaporated to dryness, and the residue from the extract was steam distilled. 7.05 parts of dicyclopentadienyl iron were obtained, i.e., a yield of 63% by weight based on the cyclopentadiene available.

Dicyclopentadienyl iron can also be prepared from the iron carbonyl-cyclopentadiene complex by heating it in a mineral white oil-at C.

Example IV 23.9 parts of the iron carbonyl-cyclopentadiene complex prepared in Example I and 14.7 parts of cyclopentadiene were heated at 196 C. for 6 hours in an autoclave previously flushed out with nitrogen. After cooling, the

reaction products were Worked up as described in Example III and 10.8 parts of dicyclopentadienyl iron were obtained.

The method of Example IV can also be carried out in an evacuated autoclave.

We claim as our invention:

1. A compound composed only of the elements iron, carbon, hydrogen and oxygen, having a melting point of about 193 C., and prepared by heating together cyclopentadiene and iron pentacarbonyl at a temperature of from about 100 C. to about 200 C.

2. A process for preparing an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen, said process comprising heating together at a temperature of from about 100 C. to about 200 C. a mixture of iron pentacarbonyl and a cyclodiene of the group consisting of cyclopentadiene and hydrocarbonsubstituted cyclopentadienes and recovering from the resulting reaction mixture an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen.

3. The product produced in accordance with the process of claim 2.

4. A process for preparing an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen, said process comprising heating together at a temperature of from about 100 C. to about 200 C. in an inert atmosphere a mixture of iron pentacarbonyl and a cyclodiene of the group consisting of cylcopentadiene and hydrocarbon-substituted cyclopentadienes and recovering from the resulting reaction mixture an organoiron compound composed only of the elements iron carbon, hydrogen and oxygen.

5. A process for preparing an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen, said process comprising heating together at a temperature of from about C. to about 200 C. a mixture of iron pentarcarbonyl and a cyclodiene of the group consisting of cyclopentadiene and hydrocarbonsubstituted cyclopentadienes in an atmosphere Whose major component is said cyclodiene and Whose minor component is an inert gas and recovering from the resulting reaction mixture an organo-iron compound composed only of the elements, iron, carbon, hydrogen and oxygen.

6. A process for preparing an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen, said process comprising heating together at a temperature of from about 100 C. to about 200 C. in the absence of molecular oxygen, a mixture of iron pentacarbonyl and a cyclodiene of the group consisting of cyclopentadiene and hydrocarbon-substituted cyclopentadienes and recoveiing from the resulting reaction mixture an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen.

7. A process for preparing an organo-iron compound composed only of the elements iron, carbon, hydrogen and oxygen, said process comprising heating together at a temperature of from about 100 C. to about 200 C. a mixture of iron pentacarbonyl and cyclopentadiene and recovering from the resulting reaction mixture an organoiron compound composed only of the elements iron, carbon, hydrogen and oxygen.

References Cited in the file of this patent UNITED STATES PATENTS Veltman Oct. 8, 1946 Catlin et a1. Oct. 22, 1957 OTHER REFERENCES UNITED STATES PATENT OFFICE sErmcArwN conEsHoN Patent No 2,898 359 August 4 1959 Kenneth Leedham et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and tha'; the said Letters Patent should read as corrected below.

Column 1 v line 71 the formula should appear as shown below instead of as in the patent:

Signed and sealed this 2nd day of May 19610 (SEAL) Attest:

ERNEST We SWIDER DAVID L, LADD Attesting Gfficer Commissioner of Patents 

2. A PROCESS FOR PREPARATING AN ORGANO-IRON COMPOUND COMPOSED ONLY OF THE ELEMENTS IRON, CARBON, HYDROGEN AND OXYGEN, SAID PROCESS COMPRISING HEATING TOGETHER AT A TEMPERATURE OF FROM ABOUT 100*C. TO ABOUT 200*C. A MIXTURE OF IRON PENTACARBONYL AND A CYCLODIENE OF THE GROUP CONSISTING OF CYCLOPENTADIENE AND HYDROCARBONSUBSTITUTED CYCLOPENTADIENES AND RECOVERING FROM THE RESULTING REACTION MIXTURE AN ORGANO-IRON COMPOUND COMPOSED ONLY OF THE ELEMENTS IRON, CARBON, HYDROGEN AND OXYGEN. 